This invention relates to blends of cycloaliphatic epoxy resins and epoxidized low viscosity polydiene polymers which are used for structural adhesives, coatings, electrical castings, encapsulants, potting compounds, laminates, and construction adhesives. More specifically, the invention relates to the use of epoxidized low viscosity polydiene polymers as toughening modifiers for cycloaliphatic epoxy resins.
Cycloaliphatic epoxy resins are generally known to be useful in a wide range of products such as filament-wound composites, as encapsulants for electrical products and in adhesives and coatings. Such resins include the Union Carbide Cycloaliphatic Epoxides and CYRACURE.RTM. resins. Cycloaliphatic epoxy resins have the disadvantage that they are very brittle when cured. This brittleness makes them unsuitable for many applications including in coatings where brittleness leads to poor adhesion, in structural adhesives where brittleness causes poor impact resistance and in electrical encapsulants where brittleness leads to poor thermal shock resistance. In a recent development, it was found that by blending the cycloaliphatic epoxy resins with specified low viscosity epoxidized polydienes a degree of flexibility could be imparted to these cycloaliphatic epoxy resins while retaining most, if not all, of their advantageous characteristics. These compositions are useful in many applications. However, because their flexibility and ability to adhere to substrates such as metals are lower than desired, they are not as suitable for use as impact resistant adhesives and coatings. The present invention provides an improved composition which is more flexible and adheres better to metals.